Signal modulation

ABSTRACT

According to an embodiment of the invention, a method and apparatus for signal modulation are described. According to an embodiment of the invention, a method comprises producing and transferring a modulated signal. The modulation of the signal is over a plurality of amplitude levels, including at least a first amplitude level, a second amplitude level and a third amplitude level, and over a plurality of time slots, including at least a first time slot, a second time slot, and a third time slot. The modulated signal transitions from the first amplitude level to the second amplitude level in the first phase slot, remains at the second amplitude level in the second time slot, and transitions from the second amplitude level to the third amplitude level in a third time slot.

FIELD

An embodiment of the invention relates to signaling in general, and morespecifically to signal modulation.

BACKGROUND

In signal operations, numerous different modulation methods may beimplemented. In certain cases, a modulation scheme may providemodulation in which a change of a signal in a first modulation mode doesnot affect or does not greatly affect the signal in a second modulationmode. Such a signal may be described as being orthogonal. For example, asignal may be modulated such that both the phase and amplitude of thesignal are modulated, the signal amplitude being a first modulation modeand the signal phase being a second modulation mode.

However, conventional modulation of signals does not utilize allpossible signal combinations. For example, the symbols utilized inmodulation of a signal in amplitude and phase generally is limited to asingle amplitude transition. For this reason, the amount of informationthat may be contained in such a modulated signal is limited.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. In the drawings:

FIG. 1 illustrates an embodiment of signal transmission or transferbetween a first agent and a second agent;

FIG. 2 is an illustration of certain symbols for a modulation scheme;

FIG. 3 illustrates certain symbols that may be generated in anembodiment of a modulation scheme;

FIG. 4 illustrates additional symbols that may be generated in anembodiment of a modulation scheme;

FIG. 5 illustrates certain symbols for an embodiment of a modulationscheme that includes staircase modulation;

FIG. 6 illustrates additional symbols for an embodiment of a modulationscheme that includes staircase modulation;

FIG. 7 is a diagram illustrating an embodiment of signal generation;

FIG. 8 is a diagram illustrating an embodiment of signal generation fora modulation scheme that includes staircase modulation;

FIG. 9 is a diagram illustrating an embodiment of a device for producingmodulated signals; and

FIG. 10 is an illustration of an embodiment of a computer environment.

DETAILED DESCRIPTION

A method and apparatus are described for orthogonal signal modulation.

Before describing an exemplary environment in which various embodimentsof the present invention may be implemented, some terms that will beused throughout this application will briefly be defined:

As used herein, “orthogonal” describes a signal is modulated in amultiple modes and the modulation modes are largely mutuallyindependent. The term indicates that a change in a first modulation modehas no effect or a limited effect on a second modulation mode. Amongothers examples, the term includes the modulation of a signal inamplitude and phase.

As used herein, “modulation” means a process by which an informationsignal is used to modify a characteristic of another signal. Stated inan alternative manner, modulation is a process by which signalcharacteristics are transformed to represent information or data.

According to an embodiment of the invention, symbols that may beutilized in a modulation scheme are expanded to include additionalusable symbols. Under a particular embodiment of the invention, themodulation of a signal includes modulation in a staircase manner.

According to an embodiment of the invention, usable symbols included inthe spectrum of states provided by orthogonal modulation schemes areexpanded. For example, a particular modulation scheme may include aplurality of differentiable voltage states and a plurality ofdifferentiable phase states or time slots. A conventional modulationscheme will utilize only a limited number of such states. In the generalcase, in which there are x states in one modulation dimension and ystates in another modulation dimension, the number of possible states isequal to x^(y)−1 possible states. In the particular example of 3differentiable voltage states and 4 differentiable phase states, thetotal number of available differentiable states is (3⁴−1) or 80 possiblestates. Under an embodiment of the invention, additional states are usedin a modulation scheme to carry extra information. The additional statesmay be limited to states that do not create circuit or channeldifficulties.

If a modulation scheme is orthogonal, a bit of modulation may be addedin a first dimension without directly impacting a second dimension. Abit may be encoded as a pair of differentiable states, and thus adding abit to a modulation system therefore doubles the number of requireddifferentiable states. For example 1 bit requires 2 states, 2 bitsrequire 4 states, and continuing in this manner. As additional bits areadded, the number of differentiable states grows exponentially. Usingorthogonal modulation may lessen the effect of the exponential increaseby encoding bits along multiple exponentials without proceeding too farwith each exponential. For example, 1 bit of amplitude modulationrequires 2 differentiable voltage states (plus an initial third state toprovide a voltage transition).

It is possible to add another bit to a modulation scheme by doubling thenumber of differentiable voltage states. However, this result may alsobe obtained by retaining the same number of voltage states but adding abit of phase modulation. The advantage of the latter process is that theresulting system will not require a more sensitive voltage receiver andwill not need to operate with a lower signal to noise ratio that wouldresult from the smaller transitions between amplitude states. Forsimplicity the examples shown in this application show orthogonalmodulation that utilizes only signal amplitude and signal phase, butembodiments of the invention are not limited this particularimplementation.

FIG. 1 illustrates an embodiment of a system in which modulated signalsare transmitted or transferred between two agents. In this system, afirst agent 105 and a second agent 110 transfer signals. The agents maybe any devices or components that transmit and receive signals.According to one embodiment, the signals are transmitted over acommunication channel 115. According to another embodiment, the signalsare transferred via a bus. The channel may use any medium, and thechannel may be unidirectional or bi-directional. The transmitted signals120 are modulated using some scheme to encode the signals. Themodulation scheme for the signals 120 may include orthogonal modulation,such as modulation of a signal in amplitude and phase.

FIG. 2 is an illustration of certain symbols for a modulation scheme. Inthis scheme, an orthogonal signal is encoded by a transition betweendifferent amplitudes. In addition, the signal is encoded by transitionin one of a plurality of different phases. Further, the same encoding isprovided for a leading edge of a signal and a trailing edge of thesignal, thereby multiplying the number of possible signals.

In FIG. 2, the leading edge modulation 205 and trailing edge modulation210 are shown. In the leading edge modulation 205, there is either atransition to a first amplitude 235 (shown as a “half amplitude”) or atransition to a second amplitude 225 (shown as a “full amplitude”). Inthis example, the second amplitude 235 is twice the amplitude of thefirst amplitude 225, but any number of differentiable amplitude and anynumerical relationship between the amplitudes may be present in anembodiment of the invention. The leading edge modulation 205 includesfour possible phase positions 215, indicated as phase position 0, phaseposition 1, phase position 2, and phase position 3. While theillustration includes four phase positions, an embodiment of theinvention may include any number of phase positions.

In this example, the trailing edge modulation 210 includes transitionfrom a first amplitude 240 and transition from a second amplitude 230.Further, the trailing edge modulation provides for transition in one offour different phase positions 220, phase position 0, phase position 1,phase position 2, and phase position 3. In this particular example, theamplitude levels of the leading edge modulation 205 are required tomatch the amplitude levels of the trailing edge modulation 220. Althoughthe leading edge phase positions 215 for the leading edge modulation 205match the phase positions 220 of the trailing edge modulation 210, thisis not required for every embodiment of the invention.

FIG. 2 thus demonstrates 1 bit of amplitude modulation on the leadingedge, 2 bits of phase modulation on the leading edge, and 2 bits ofphase modulation on the trailing edge. In this example the trailing edgealways returns to the initial amplitude (such as zero) and thus carriesno additional information. While this is one example, an embodiment ofthe invention may include any number of differentiable amplitudes andphase positions. Matching the four possible transitions for the firstamplitude level 235 for the leading edge modulation 205 with the fourpossible transitions for the first amplitude level 240 for the trailingedge modulation 210 provides sixteen possible states. Matching the fourpossible transitions for the second amplitude level 225 for the leadingedge modulation 205 with the four possible transitions for the secondamplitude level 230 for the trailing edge modulation 210 providessixteen additional states. The total number of states thus is 32,providing sufficient differentiable states to encode five bits ofinformation (2⁵=32).

However, the states shown in FIG. 2 do not include all possible statesfor the chosen modulation scheme. Additional states may also be shown.For example, FIG. 3 contains the same transitions shown in FIG. 2, withthe symbols 305 including transition to a first amplitude level 320(shown as a “half amplitude”) and transitions to a second amplitudelevel 310 (shown as a “full amplitude”), and four possible phasepositions 310. While the symbols shown in the embodiments of FIG. 3 andFIG. 4 illustrate leading edge modulation, trailing edge modulation maybe formed in the same manner. In FIG. 3, there are four combinationsthat transition to the first amplitude level 320 and four combinationsthat transition to the second amplitude level 315. In each symbol shownin FIG. 3 there is a single transition to an amplitude level, with thetransition occurring in one phase period.

However, FIG. 4 illustrates additional symbols that may be generated inan embodiment of a modulation scheme. For the illustrated symbols 405,there are again four possible phase positions 410. In a first set ofmodulation states, a staircase modulation 415 is provided in which atransition is made from the initial amplitude level to the firstamplitude level in a first phase and a transition from the firstamplitude level to the second amplitude level in another phase, with atleast one intervening phase between the transitions in which theamplitude is unchanged. For example, symbol 9 provides for a transitionfrom the initial amplitude to the first amplitude level in phaseposition 0, maintenance of the first amplitude level in phase position1, a transition from the first amplitude level to the second amplitudelevel in phase position 2, and maintenance of the second amplitude levelin phase position 3. Symbol 10 for provides for a transition from theinitial amplitude to the first amplitude level in phase position 0,maintenance of the first amplitude level in phase positions 1 and 2, anda transition from the first amplitude level to the second amplitudelevel in phase position 3. Symbol 11 provides for maintenance of theinitial amplitude level in phase position 0, a transition from theinitial amplitude to the first amplitude level in phase position 1,maintenance of the first amplitude level in phase position 2, and atransition from the first amplitude level to the second amplitude levelin phase position 3.

A second set of possible symbols utilizing staircase modulation 420 isalso possible in an embodiment of the invention. However, such symbolsdo not provide an intervening period in which the amplitude isunchanged. As shown in FIG. 4, symbol 12 provides for a transition fromthe initial amplitude to the first amplitude level in phase position 0and a transition from the first amplitude level to the second amplitudelevel in phase position 1. Similarly, symbol 13 provides for atransition from the initial amplitude to the first amplitude level inphase position 1 and a transition from the first amplitude level to thesecond amplitude level in phase position 2, and symbol 14 provides for atransition from the initial amplitude to the first amplitude level inphase position 2 and a transition from the first amplitude level to thesecond amplitude level in phase position 3.

There are additional signal possibilities 430 under embodiments that donot follow the same modulation patterns as the prior examples. Forexample, symbol 15 provides for a transition from the initial amplitudeto the first amplitude level in phase position 0 and a transition backfrom the first amplitude level to the initial amplitude level in phaseposition 1. Symbol 16 provides for a transition from the initialamplitude to the first amplitude level in phase position 0, maintenanceof the first amplitude in phase position 1, and a transition back fromthe first amplitude level to the initial amplitude level in phaseposition 2. Symbols 17 and 18 provide additional examples, and there areother possibilities that may be provided.

Generally, if the circuitry to differentiate 3 voltage levels (1 bit or2 states) and the circuitry to differentiate 4 phase slots has beenconstructed, then the circuitry required to differentiate 2 voltagelevels in each of the 4 phase slots is largely in place. Therefore, itis possible that any of the states shown in FIGS. 3 and 4 may bedifferentiated by a receiver with the same or similar circuitry andtolerances as used to receive the states illustrated in FIG. 2.

However, not all waveforms have the same frequency content. Themodulation of the states shown in FIG. 2 may be accomplished in the lowfrequency, pass band of a channel. The phase slots for a channel may bemuch narrower than the minimum pulse width for the channel. If a signaltransitions from a reference voltage level to a new voltage level andthen back to the reference level in the time domain of a phase slot,information is encoded at a much higher frequency than the pulse widthbase band. This is true of waveforms such as symbols 15-18 of FIG. 4.However, if decomposed, the frequency content of symbols 9-11 and 12-14of FIG. 4, representing staircase modulation, is relatively low. Thetransitions for such symbols are monotonic (always increasing ordecreasing) and thus the waveform is similar to a slowly risingtransition. The frequency content of a symbol may be estimated torelative to 0.2/T rise, with the symbols 9-11 and 12-14 of FIG. 4 havingrelatively long rise times.

Another issue regards inter-symbol interference (ISI). Not all signalshave the same immunity to inter-symbol interference (ISI). Symbols 1-4and 5-7 of FIG. 3 have only a single transition followed by a relativelylong pulse width. This length of time allows ringing caused by the firsttransition to die down before another transition occurs or is expected.In contrast, symbols 12-14 of FIG. 4 have a first transition followedimmediately by a second transition. This also true of symbol 15 and 18.The closely spaced transitions may introduce inter-symbol interferencefrom the first transition onto the second transition. However, symbols9-11 of FIG. 4 have at least one phase slot between transitions, whichmay lessen the level of ISI.

FIGS. 5 and 6 illustrate signal modulation according to an embodiment ofthe invention that includes the use of staircase modulation, such as thestaircase modulation 415 illustrated in FIG. 4. The modulation schemeprovides for 11 different symbols for the leading edge and 11 differentsymbols for the trailing edge. In this example, modulation of theleading edge 505 and the trailing edge 510 are shown. The exampleprovides for four possible phase positions for the leading edge 515 andfour possible phase positions for the trailing edge 520, although it isnot necessary for the leading edge phase positions and the trailing edgephase positions to be equal in number in all embodiments of theinvention. There are two signal amplitudes (plus a third initial signalamplitude), with the first, smaller signal amplitude shown in FIG. 6 andthe second, larger signal amplitude shown in FIG. 5. In thisillustration, the first amplitude provides a half amplitude signal andthe second amplitude provides a full amplitude signal. In FIG. 5,symbols reaching the second amplitude for the leading edge 525 andsymbols beginning at the second amplitude for the trailing edge 530 areillustrated. Leading edge symbols 1 through 4 illustrate signals thattransition from the initial amplitude to the second amplitude in asingle phase period, while trailing edge symbols 1 through 4 illustratesignals that transition from the second amplitude to the initialamplitude in a single phase period. Leading edge symbols 5 through 7illustrate staircase modulated signals in which a signal transitionsfrom the initial amplitude to the first amplitude in a first phaseperiod, maintains the first amplitude for one or more phase periods,including a second phase period, and transitions from the firstamplitude to the second amplitude in a third phase period. Trailing edgesymbols 5 through 7 illustrate counterpart signals for transitions fromthe second amplitude to the first amplitude and to the initialamplitude. Because of each of the leading edge symbols 505 concludes atthe second amplitude and each of the trailing edge symbols 510 commencesat the second amplitude, any of the leading edge symbols shown in FIG. 5may be matched with any the trailing edge symbols in this figure. Suchcombinations provide 7×7=49 modulation states.

In addition, FIG. 6 illustrates additional states possible for theembodiment. Symbols are illustrated for leading edge 605 and trailingedge 610. There are four possible phase positions for the leading edge615 and the trailing edge 620. The illustrated leading edge symbolsconclude at a first amplitude 625 and the trailing edge symbols commenceat the first amplitude 630. Any of the illustrated leading edge symbols,symbols 8 through 11, thus may be matched with any of the illustratedtrailing edge symbols, signals 8 through 11. The number of modulationstates shown in FIG. 6 thus is 4×4=16. The total number of modulationstates for the modulation scheme provided in the illustrated embodimentof the invention thus is 49+16=65 states. The total number of states issufficient to encode 6 bits of information, which requires 64 states(2⁶=64). Therefore, by including the staircase modulation symbols, themodulation scheme may be used to encode an additional bit ofinformation, 6 bits as opposed to 5 bits.

The modulation scheme illustrated in FIGS. 5 and 6 may provide a higherbandwidth for a given set of jitter and voltage tolerances, as comparedto conventional modulation techniques. Such higher bandwidth may beprovided without requiring significant additional effort for signaldifferentiation. Further, the increase in bandwidth may provide highersystem performance in many different environments.

FIG. 7 is a diagram illustrating an embodiment of a signal modulationoperation. As illustrated in FIG. 7, a signal is modulated with twovoltage levels (plus a third initial voltage level) and four phasepositions. In this example, the system 705 chooses a phase for thesignal modulation. The block diagram shows a multiplexer 710, althoughthis physical device and the other physical devices shown in FIG. 7 maynot be used in an embodiment of the invention. The multiplexer 710receives a phase selection signal 720, which would comprise 2 bits forthe four phase positions. A signal for the chosen phase signal is thenprovided to a clock input of a first logic device 725 and a second logicdevice 730. When the devices are clocked the signal representing thephase, either a signal for a first amplitude, shown as V1 735, or asignal for a second amplitude, shown as V2 740, is directed to a signalgenerator 745 that generates a signal with the chosen modulation. Themodulated signal then is transferred over a communication channel 750 toanother component or device. The modulation of the trailing edge may beencoded similarly, with the phase choice signal 720 then representingthe phase position to provide a transition to the initial signalamplitude. The illustrated embodiment provides for only a singletransition to either a first signal amplitude or a second signalamplitude, and thus is not sufficient for a modulation scheme thatincludes staircase modulation.

FIG. 8 illustrates an embodiment of signal modulation operation thatincludes staircase modulation. In this example, a first multiplexer 810chooses a phase position for a transition to a first amplitude and asecond multiplexer 815 chooses a phase position for a transition to asecond amplitude. The first multiplexer 810 receives a first phaseselection signal to choose from the phase inputs 820. The secondmultiplexer 815 receives a second phase selection signal to choose fromthe phase inputs 820. In the case of a single transition in a symbol,only one of the multiplexers will be activated. In the case of astaircase modulation, both multiplexers will be activated. The firstmultiplexer 810 provides a clock input to a first logic device 840,which receives a first amplitude signal V1 850. The second multiplexer810 provides a clock input to a second logic device 840, which receivesa second amplitude signal V2 855. The outputs of the first logic device840 and the second logic device 840 are provided to a signal generator860, which generates a modulated signal to be transferred over acommunication channel 865. Because of the multiple phase selections, thesystem illustrated in FIG. 8 can produce staircase modulation.

FIG. 9 illustrates an embodiment of a unit to generate a modulatedsignal. The illustration provided is a functional block diagram toillustrate the signal modulation operation, but a modulated signal maybe generated by any known method, circuit, or device. In thisillustration, a generator unit 905 receives two inputs, a signal for afirst amplitude V1 910 and a signal for a second amplitude V2 915.Functionally, the signals, how shown as V1 920 and V2 930, control twoswitches. An active V1 920 activates a first switch 950, which providesa path from current from a first current source 935 through a load 945,shown as a 50-ohm resistor. The first current times the load resistancethen provides a voltage drop equal to the first signal amplitude. Anactive V2 920 activates a second switch 955, which provides a path fromcurrent from a second current source 935 through the load 945, with thesecond current times the load resistance equaling the second signalamplitude. In an alternative embodiment, a first signal turns on a firstswitch and a second signal turns on both switches, with the same signalmodulation being provided. The modulated signal is then provided to theoutput 950.

Techniques described here may be used in many different environments.FIG. 10 is block diagram of an exemplary computer that may be used inconjunction with an embodiment of the invention. Under an embodiment ofthe invention, the computer may comprise an embedded system or otherspecial purpose computer. An embedded system or other special purposecomputer may operate without certain of the components and featuresdescribed herein. An embodiment of the invention may be utilized for thetransfer of signals between components or devices in the exemplarycomputer.

Under an embodiment of the invention, a computer 1000 comprises a bus1005 or other communication means for communicating information, and aprocessing means such as one or more processors 1010 (shown as 1011,1012 and continuing through 1013) coupled with the first bus 1005 forprocessing information.

The computer 1000 further comprises a random access memory (RAM) orother dynamic storage device as a main memory 1015 for storinginformation and instructions to be executed by the processors 1010. Mainmemory 1015 also may be used for storing temporary variables or otherintermediate information during execution of instructions by theprocessors 1010. The computer 1000 also may comprise a read only memory(ROM) 1020 and/or other static storage device for storing staticinformation and instructions for the processor 1010.

A data storage device 1025 may also be coupled to the bus 1005 of thecomputer 1000 for storing information and instructions. The data storagedevice 1025 may include a magnetic disk or optical disc and itscorresponding drive, flash memory or other nonvolatile memory, or othermemory device. Such elements may be combined together or may be separatecomponents, and utilize parts of other elements of the computer 1000.

The computer 1000 may also be coupled via the bus 1005 to a displaydevice 1030, such as a liquid crystal display (LCD) or other displaytechnology, for displaying information to an end user. In someenvironments, the display device may be a touch-screen that is alsoutilized as at least a part of an input device. In some environments,display device 1030 may be or may include an auditory device, such as aspeaker for providing auditory information. An input device 1040 may becoupled to the bus 1005 for communicating information and/or commandselections to the processor 1010. In various implementations, inputdevice 1040 may be a keyboard, a keypad, a touch-screen and stylus, avoice-activated system, or other input device, or combinations of suchdevices. Another type of user input device that may be included is acursor control device 1045, such as a mouse, a trackball, or cursordirection keys for communicating direction information and commandselections to processor 1010 and for controlling cursor movement ondisplay device 1030.

A communication device 1050 may also be coupled to the bus 1005.Depending upon the particular implementation, the communication device1050 may include a transceiver, a wireless modem, a network interfacecard, or other interface device. The computer 1000 may be linked to anetwork or to other devices using the communication device 1050, whichmay include links to the Internet, a local area network, or anotherenvironment.

In the description above, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the present invention may be practicedwithout some of these specific details. In other instances, well-knownstructures and devices are shown in block diagram form.

The present invention may include various processes. The processes ofthe present invention may be performed by hardware components or may beembodied in machine-executable instructions, which may be used to causea general-purpose or special-purpose processor or logic circuitsprogrammed with the instructions to perform the processes.Alternatively, the processes may be performed by a combination ofhardware and software.

Portions of the present invention may be provided as a computer programproduct, which may include a machine-readable medium having storedthereon instructions, which may be used to program a computer (or otherelectronic devices) to perform a process according to the presentinvention. The machine-readable medium may include, but is not limitedto, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks,ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, flash memory, orother type of media/machine-readable medium suitable for storingelectronic instructions. Moreover, the present invention may also bedownloaded as a computer program product, wherein the program may betransferred from a remote computer to a requesting computer by way ofdata signals embodied in a carrier wave or other propagation medium viaa communication link (e.g., a modem or network connection).

Many of the methods are described in their most basic form, butprocesses may be added to or deleted from any of the methods andinformation may be added or subtracted from any of the describedmessages without departing from the basic scope of the presentinvention. It will be apparent to those skilled in the art that manyfurther modifications and adaptations may be made. The particularembodiments are not provided to limit the invention but to illustrateit. The scope of the present invention is not to be determined by thespecific examples provided above but only by the claims below.

It should also be appreciated that reference throughout thisspecification to “one embodiment” or “an embodiment” means that aparticular feature may be included in the practice of the invention.Similarly, it should be appreciated that in the foregoing description ofexemplary embodiments of the invention, various features of theinvention are sometimes grouped together in a single embodiment, figure,or description thereof for the purpose of streamlining the disclosureand aiding in the understanding of one or more of the various inventiveaspects. This method of disclosure, however, is not to be interpreted asreflecting an intention that the claimed invention requires morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the claimsare hereby expressly incorporated into this description, with each claimstanding on its own as a separate embodiment of this invention.

1. A method comprising: producing a modulated signal, the modulatedsignal being modulated over a plurality of amplitude levels, includingat least a first amplitude level, a second amplitude level and a thirdamplitude level, and over a plurality of time slots, including at leasta first time slot, a second time slot, and a third time slot, themodulated signal: transitioning from the first amplitude level to thesecond amplitude level in the first phase slot, remaining at the secondamplitude level in the second time slot, and transitioning from thesecond amplitude level to the third amplitude level in the third timeslot; and transferring the modulated signal.
 2. The method of claim 1,wherein the modulated signal is orthogonal.
 3. The method of claim 1,wherein producing the modulated signal further comprises remaining atthe second amplitude level for a plurality of time slots.
 4. The methodof claim 1, wherein producing the modulated signal further comprises:transitioning from the third amplitude level to the second amplitudelevel in a fourth phase slot, remaining at the second amplitude level ina fifth time slot, and transitioning from the second amplitude level tothe first amplitude level in a sixth time slot.
 5. The method of claim1, wherein producing the modulated signal further comprisestransitioning from the third amplitude level to an amplitude level otherthan the first amplitude level.
 6. The method of claim 1, wherein atransition between amplitude levels occurs over a plurality of timeslots.
 7. The method of claim 1, wherein transferring the modulatedsignal comprises transmitting the modulated signal over a communicationchannel.
 8. The method of claim 1, wherein transferring the modulatedsignal comprises transferring the modulated signal over a bus.
 9. Amethod comprising: generating a modulated signal using a firstmodulation mode and a second modulation mode, the first modulation modehaving a plurality of different positions including at least a firstposition, a second position, and a third position, the second modulationmode having a plurality of different positions, including at least afirst position, a second position, and a third position; the modulatedsignal transitioning from the first position to the second position ofthe first modulation mode while in the first position of the secondmodulation mode; the modulated signal remaining in the second positionof the first modulation mode while in the second position of the secondmodulation mode; and the modulated signal transitioning from the secondposition to the third position of the first modulation mode while in thethird position of the second modulation mode.
 10. The method of claim 9,further comprising transferring the modulated signal over acommunication channel.
 11. The method of claim 9, wherein the firstmodulation mode comprises signal amplitude.
 12. The method of claim 11,wherein the second modulation mode comprises signal phase.
 13. Themethod of claim 9, wherein the modulated signal is orthogonal.
 14. Themethod of claim 9, wherein the modulated signal further: transitionsfrom the third position to the second position of the first modulationmode while in a fourth position of the second modulation mode; remainsin the second position of the first modulation mode while in a fifthposition of the second modulation mode; and transitions from the secondposition to the first position of the first modulation mode while in asixth position of the second modulation mode.
 15. The method of claim 9,wherein the modulated signal further transitions from the third positionof the first modulation mode to a position other than the secondposition of the first modulation mode.
 16. The method of claim 9,wherein a transition between positions of the first modulation modeoccurs over a plurality of positions of the second modulation mode. 17.A method comprising: producing a modulated signal, the modulated signal,the modulated signal being modulated over a plurality of amplitudelevels, including at least a first amplitude level, a second amplitudelevel, and a third amplitude level, and over a plurality of phase slots,including at least a first phase slot, a second phase slot, and a thirdphase slot, the modulated signal: transitioning from the first amplitudelevel to the second amplitude level in the first phase slot, remainingat the second amplitude level in the second time slot, and transitioningfrom the second amplitude level to the third amplitude level in thethird time slot; transferring the modulated signal; receiving themodulated signal; and demodulating the modulated signal.
 18. The methodof claim 17, wherein the modulated signal is orthogonal.
 19. The methodof claim 17, wherein the modulated signal remains at the secondamplitude level for a plurality of phase slots.
 20. The method of claim17, wherein the modulated signal further transitions from the thirdamplitude level to the first amplitude level in a fourth phase slot. 21.The method of claim 17, wherein the modulated signal further transitionsfrom the third amplitude level to the second amplitude level in a fourthphase slot, remains at the second amplitude level in a fifth phase slot,and transitions from the second amplitude level to the first amplitudelevel in a sixth phase slot.
 22. The method of claim 17, wherein themodulated signal further transitions from the third amplitude level to alevel other than the first amplitude level.
 23. The method of claim 17,wherein a transition between amplitude levels occurs over a plurality ofphase slots.
 24. A method comprising: obtaining a data signal;modulating the data signal to form a modulated signal, the modulatedsignal being one of a plurality of modulated signals, the plurality ofmodulated signals being modulated over amplitude levels, including atleast a first amplitude level, a second amplitude level, and a thirdamplitude level, and over phase slots, the plurality of modulatedsignals comprising: a signal that: transitions from the first amplitudelevel to the second amplitude level in one of a first plurality of phaseslots; and transitions from the second amplitude level to the firstamplitude level in one of a second plurality of phase slots; and asignal that: transitions from the first amplitude level to a thirdamplitude level in one of the first plurality of phase slots; ortransitions from the first amplitude level to the second amplitude levelin a first slot of the first plurality of phase slots, remains at thesecond amplitude level for a second slot of the first plurality of phaseslots, and transitions from the second amplitude level to the thirdamplitude level in a third slot of the first plurality of phase slots;and transitions from the third amplitude level to the first amplitudelevel in one of the second plurality of phase slots; or transitions fromthe third amplitude level to the second amplitude level in a first slotof the second plurality of phase slots, remains at the second amplitudelevel for a second slot of the second plurality of phase slots, andtransitions from the second amplitude level to the first amplitude levelin a third slot of the second plurality of phase slots.
 25. The methodof claim 24, wherein the modulated signal is orthogonal.
 26. The methodof claim 24, further comprising transferring the modulated signal from afirst unit to a second unit over a communication channel.
 27. The methodof claim 24, wherein the plurality of modulated signals further includesa signal that transitions to the third amplitude level, and thentransitions from the third amplitude to a level other than the firstamplitude level.
 28. The method of claim 24, wherein a transitioningbetween amplitude levels occurs over a plurality of phase slots.
 29. Adevice comprising: an output to a communication channel; and a signalgenerator to produce a modulated signal on the communication channel,the modulated signal comprising: a first modulation mode, the modulatedsignal having a plurality of possible positions in the first modulationmode, and a second modulation mode, the modulated signal having aplurality of possible positions in the second modulation mode; themodulated signal transitioning from a first position to a secondposition in the first modulation mode while in a first position of thesecond modulation mode; the modulated signal remaining in the secondposition in the first modulation mode while in a second position of thesecond modulation mode; and the modulated signal transitioning from thesecond position to a third position in the first modulation mode whilein a third position of the second modulation mode.
 30. The device ofclaim 29, wherein the first modulation mode comprises signal amplitude.31. The device of claim 30, wherein the second modulation mode comprisessignal phase.
 32. The device of claim 29, wherein the modulated signalis orthogonal.
 33. A system comprising: a communication channel; a firstdevice to transfer a modulated signal over the communication channel,the modulated signal: transitioning from a first amplitude level to asecond amplitude level in a first phase slot, remaining at the firstamplitude level in a second time slot, and transitioning from the secondamplitude level to a third amplitude level in a third time slot; and asecond device to receive the modulated signal over the communicationchannel.
 34. The system of claim 33, wherein the modulated signal isorthogonal.
 35. The system of claim 33, wherein the modulated signalremains at the first amplitude level for a plurality of time slotsbefore transitioning to the second amplitude level.